1. Field of the Invention
The invention relates to a screw press having a flywheel rotationally connected to the spindle by way of a friction coupling and a spindle displaceable axially in a nut mounted in the upper cross member of the press frame, wherein the flywheel has external toothing to a width corresponding to the maximum press stroke plus the width of the driving pinion, a plurality of pinions engaging in the said toothed rim are each driven by oil-hydraulic axial piston motors or by a pair of oil-hydraulic axial piston motors and the axial piston motors together with the pinions are disposed on a platform surrounding the upper cross member of the press frame.
2. Description of the Prior Art
Screw presses, which are preferably used as drop-forging machines on account of their design advantages, are restricted in their impact force by friction wheel drive (friction screw presses), and therefore screw presses with an impact strength of from 40 MN (Meganewtons) are frequently provided, and screw presses with an impact of from 80 MN are in general provided, with a gearwheel drive, for which purpose the flywheel has external toothing and has motor-driven pinions engaging in its toothed rim. Electric motors or oil-hyraulic motors are used for driving the pinions.
Electric drive has the advantage of simpler energy supply, but high peak currents occur since the necessary energy to be stored in the flywheel must be applied within the short period of the stroke in which the flywheel is to be accelerated to the required rotational speed.
Special arrangements are therefore frequently necessary for limiting the peak currents, and this renders the plant expensive and leads to a prolongation of the cycle time. Since the electric motors are twice accelerated from rest to the required rotational speed and braked again during each operating cycle, correspondingly high current heat losses are unavoidable and also the idle power absorbed by the motor is disadvantageous. The torque to be applied necessitates correspondingly large and heavy motors which, apart from the fact that they have an unfavorable ratio of torque to moment of inertia, lead to the structural disadvantage that the spindle together with the flywheel and toothed rim must be mounted axially non-displaceably in the upper cross member of the press frame and the spindle nut must be mounted in the slide of the press, and this results in unfavorable exposure of the spindle to pressure and torsion.
Oil-hydraulic motors, in particular axial piston motors, have a subtantially lower specific weight with small dimensions than electric motors, so that they can be arranged, individually or in pairs, on diametrically opposite a driving pinion, with the further structural advantage that the spindle together with the flywheel and the toothed rim can be mounted axially displaceably in a nut mounted in the upper cross member of the press frame and are thus exposed only to torsion above the nut and only to thrust below the nut. In order to supply the oil-hydraulic motors, an oil station is required which comprises an electric motor, oil pump, high-pressure accumulator and control devices as well as devices for filtering and cooling the oil, and which in addition to the press is disposed on the workplace floor, in a basement or on a scaffold and is connected to the oil-hydraulic motors by way of flexible high-pressure ducts which compensate for the movements of the press. The structural expenditure for this is considerable, in particular when subject to the requirements of operational reliability.